The present disclosure relates to a memory element including a memory layer to store the information of the magnetization state of a ferromagnetic layer and a magnetization pinned layer, in which the direction of magnetization is pinned, wherein the direction of magnetization of the memory layer is changed by passing a current and a memory device provided with this memory element.
Regarding information apparatuses, e.g., computers, DRAM with high-speed operation and high density has been used widely as random access memory.
However, the dynamic random access memory (DRAM) is a volatile memory in which the information disappears when the power is turned off. Consequently, a nonvolatile memory, in which the information does not disappear, has been desired.
As for a candidate for the nonvolatile memory, a magnetic random access memory (MRAM), in which the information is stored through magnetization of a magnetic substance, has been noted and developed.
As for a method for storing into MRAM, a spin torque MRAM, in which magnetization of a magnetic substance responsible for memory is reversed by a spin torque passing between two magnetic substances, as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2004-193595, has been noted because the structure is relatively simple and the number of rewriting is large.
In many cases, the memory element making use of spin torque magnetization reversal is formed on the basis of magnetic tunnel junction (MTJ) in the same manner as that of MRAM. This configuration makes use of the fact that when a spin-polarized electron passing a magnetic layer pinned in some direction enters other free (the direction is not pinned) magnetic layer, a torque is given to the magnetic layer (this is may be referred to as a spin transfer torque), and the free magnetic layer is reversed when a current more than or equal to a certain threshold value is passed. Rewriting of 0/1 is performed by changing the polarity of the current.
The absolute value of the current for reversal is 1 mA or less with respect to an element on a scale of about 0.1 μm. In addition, this current value decreases in proportion to the element volume and, therefore, scaling is possible. Furthermore, a word line for generating a current magnetic field for memory, which is necessary for MRAM, is unnecessary and, therefore, there is an advantage that the cell structure becomes simple.
Hereafter, MRAM making use of the spin torque magnetization reversal is referred to as “spin torque MRAM” or “spin torque-magnetic random access memory (ST-MRAM)”. The spin torque magnetization reversal may be referred to as spin injection magnetization reversal.
As for ST-MRAM, those making use of in-plane magnetization, as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2004-193595, and those making use of perpendicular magnetization, as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2009-081215, have been developed.
Regarding ST-MRAM making use of in-plane magnetization, the degree of flexibility in material is high and a method for pinning magnetization is relatively easy. However, in the case where a perpendicular magnetic film is used, the materials having the perpendicular magnetic anisotropy are limited.
In recent years, an interface anisotropy type perpendicular magnetic film making use of perpendicular magnetic anisotropy which appears at a crystal interface between Fe and an oxide, as disclosed in, for example, Nature Materials., Vol 9, p. 721 (2010), has been noted. In the case where the interface anisotropy is used, a perpendicular magnetic film can be obtained by using an FeCoB alloy as a magnetic substance and MgO as an oxide, the compatibility between a high magnetoresistance ratio (MR ratio) and perpendicular magnetization can be ensured, so that it has a potential for both the memory layer and the magnetization pinned layer. Therefore, application to perpendicular magnetization type spin torque MRAM is expected.